ALLOSTERIC EFFECTS IN A SYNTHETIC RECEPTOR FOR ALKALI-METAL IONS AND DINITROBENZENE

A novel host is described which contains three potential binding sites, viz. a cleft and two crown ether rings. The molecule can adopt three different conformations. One of these is able to form a complex with two alkali metal ions. The binding of potassium ions is shown to be a cooperative process. The association constant of the second ion is 128 times larger than that of the first. The compound also binds 1,3-dinitrobenzene at the third site by pi-pi interactions. The complex with two potassium ions binds 1,3-dinitrobezene more strongly than does the free compound by a factor of 2-6, depending on the solvent used. This allosteric effect is caused by the conformational change which is induced by the binding of the potassium ions.